1. Field of the Invention
The present invention relates generally to the field of CCD imaging devices and, more particularly, the present invention relates to a photonic device obtained by potting a photonic element mounted on a base using a light-transmitting resin, and a process for fabricating the same.
2. Description of the Related Art
Photonic devices such as CCD (charge-coupled device) linear sensors or a CCD area sensors have been fabricated heretofore into a final product by first die bonding a chip of a photonic element inside a hollow package made of a ceramics or an epoxy resin. Then an interconnection is formed using a bonding wire, and realizing an air-tight seal by using a seal glass.
Recently, for reducing cost, photonic devices have been obtained by resin molding a photonic element and bonding wires inside the hollow portion of the hollow package described above by means of potting using a light-transmitting resin and by resin molding a photonic element and bonding wires inside a resin dam formed on an LCC (Leadless Chip Carrier) substrate by means of potting a light-transmitting resin. In the aforementioned photonic devices and the processes for producing them, however, the initial viscosity and the cured hardness of the light-transmitting resin for use in potting greatly influenced the yield, the quality, and the reliability of the resultant product. That is, for example, when the initial viscosity of the light-transmitting resin is too high gas is undesirably absorbed. For example, gas is absorbed by the base material that is used in die bonding, the residual air remaining in the interstices between the photonic element and the base, the gas included in the light-transmitting resin, the air included during potting, etc., tend to remain in the light-transmitting resin and form bubbles. Those residual bubbles result in a device having poor photosensitivity.
If the hardness after curing is too low, the surface of the light-transmitting resin is liable to be so viscous and sticky that dust particles collect and adhere. Even if attempts are made to blow off the dust particles attached to the surface by using air blowing and the like, the dust particles around the resin tend to adversely adhere thereto and cause defects. Furthermore, when the light-transmitting resin is excessively soft, an attempt to wipe off dust particles adhered to the surface by using a cotton swab (with alcohol) causes deformation of the light-transmitting resin that results in breakage or deformation of the internal bonding wires.
In contrast, if the light-transmitting resin becomes too hard after curing, the stickiness on the surface of the light-transmitting resin is reduced and the adhesion of dust particles is decreased. However, when reliability evaluation is performed at a predetermined temperature cycle, high thermal stress and the resulting strain due to high hardness causes breakage of the bonding wires and frequent internal resin cracks.